Recent quotes:

the largest inventory of the world’s objects. What’s cool is that because every object was put there by a person. It’s not the largest inventory in the way that maybe a nerd like me would get excited about. But everything that’s on there, at least one human found interesting, so there is a very good chance that at least one other human is going to find that interesting. So, it’s a good set of objects. It’s the world’s largest set of objects that people care about.
My contention is that Pinterest is one of the four ways that people find things on the Internet. The default, of course, is Googling (or—fine, Microsoft—Binging). For real-time searches, there is Twitter. For people or entities, there's Facebook. But if what you want to find are things, objects, then Pinterest is the way to go.  And they are just getting started. They've got 30 billion pins now, half of them in the last six months. They've got 750 million boards. A full 75 percent of their traffic comes from mobile devices, and according to researchers, they're the top traffic source to retailers' websites and an important secondary source after Facebook for some media sites, like Buzzfeed.